Towards an Indirect Determination of the Mass-balance Distribution of Glaciers using the Kinematic Boundary Condition

The kinematic boundary condition at the surface is utilized to arrive at an estimate of the mass-balance distribution of the ablation region of Unteraargletscher, Bernese Alps, Switzerland. This is achieved without the use of any ground measurements. The terms of the kinematic boundary condition, involving surface-altitude changes with time, surface slopes, and horizontal surface velocities, are determined using high precision aerial photogrammetry. Estimating the vertical velocity distribution along the surface poses a major problem. Different approaches to solving this problem are discussed, and the potential of one particular approach is evaluated. This approach is, in essence, based on the assumption that the variation of vertical strain rates with depth is simple. The accuracy of the resulting indirect estimate of the mass balance distribution is assessed by a comparison with results from stake measurements made at about 40 different points at the surface. Although calculated values of mass balance are found to be within a reasonable range, they differ, as a function of altitude, in a systematic fashion from stake values. This suggests that the vertical strain-rate variation with depth is too complex to be parameterized in a simple manner.     

Permeable Asphalt: A New Tool to Reduce Road Salt Contamination of Groundwater in Urban Areas

Chloride contamination of groundwater in urban areas due to deicing is a well‐documented phenomenon in northern climates. The objective of this study was to evaluate the effects of permeable pavement on degraded urban groundwater. Although low impact development practices have been shown to improve stormwater quality, no infiltration practice has been found to prevent road salt chlorides from entering groundwater. The few studies that have investigated chlorides in permeable asphalt have involved sampling directly beneath the asphalt; no research has looked more broadly at surrounding groundwater conditions. Monitoring wells were installed upgradient and downgradient of an 860 m² permeable asphalt parking lot at the University of Connecticut (Storrs, Connecticut). Water level and specific conductance were measured continuously, and biweekly samples were analyzed for chloride. Samples were also analyzed for sodium (Na), calcium (Ca), and magnesium (Mg). Analysis of variance analysis indicated a significantly (p < 0.001) lower geometric mean Cl concentration downgradient (303.7 mg/L) as compared to upgradient (1280 mg/L). Concentrations of all alkali metals increased upgradient and downgradient during the winter months as compared to nonwinter months, indicating that cation exchange likely occurred. Despite the frequent high peaks of chloride in the winter months as well as the increases in alkali metals observed, monitoring revealed lower Cl concentrations downgradient than upgradient for the majority of the year. These results suggest that the use of permeable asphalt in impacted urban environments with high ambient chloride concentrations can be beneficial to shallow groundwater quality, although these results may not be generalizable to areas with low ambient chloride concentrations.     

Development and Re‐Evaluation of Tourmaline Reference Materials for In Situ Measurement of Boron δ Values by Secondary Ion Mass Spectrometry

Six tourmaline samples were investigated as potential reference materials (RMs) for boron isotope measurement by secondary ion mass spectrometry (SIMS). The tourmaline samples are chemically homogeneous and cover a compositional range of tourmaline supergroup minerals (primarily Fe, Mg and Li end‐members). Additionally, they have homogeneous boron delta values with intermediate precision values during SIMS analyses of less than 0.6‰ (2s). These samples were compared with four established tourmaline RMs, that is, schorl IAEA‐B‐4 and three Harvard tourmalines (schorl HS#112566, dravite HS#108796 and elbaite HS#98144). They were re‐evaluated for their major element and boron delta values using the same measurement procedure as the new tourmaline samples investigated. A discrepancy of about 1.5‰ in δ¹¹B was found between the previously published reference values for established RMs and the values determined in this study. Significant instrumental mass fractionation (IMF) of up to 8‰ in δ¹¹B was observed for schorl–dravite–elbaite solid solutions during SIMS analysis. Using the new reference values determined in this study, the IMF of the ten tourmaline samples can be modelled by a linear combination of the chemical parameters FeO + MnO, SiO₂ and F. The new tourmaline RMs, together with the four established RMs, extend the boron isotope analysis of tourmaline towards the Mg‐ and Al‐rich compositional range. Consequently, the in situ boron isotope ratio of many natural tourmalines can now be determined with an uncertainty of less than 0.8‰ (2s).     

Pure elastic stiffness of sand represented by response envelopes derived from cyclic triaxial tests with local strain measurements

Acta Geotechnica - The elastic stiffness of a fine sand at small to moderate strains ( $$\varepsilon \le 2 \times 10^{-4}$$ ) has been studied based on cyclic triaxial tests on cube-shaped samples...     

Biotite Reference Materials for Secondary Ion Mass Spectrometry 18O/16O Measurements

Five new biotite reference materials were calibrated at the SwissSIMS laboratory (University of Lausanne) for oxygen isotope determination by secondary ion mass spectrometry (SIMS) and are available to the scientific community. The oxygen isotope composition of the biotites, UNIL_B1 to B5, was determined by laser‐heating fluorination to be 11.4 ± 0.11‰, 8.6 ± 0.15‰, 6.1 ± 0.04‰, 7.1 ± 0.05‰ and 7.6 ± 0.04‰, respectively. SIMS analyses on spots smaller than 20 μm gave a measurement repeatability of 0.3‰ (2 standard deviation, 2s). The matrix effect due to solid solution in natural biotite could be expressed as a linear function of X_Mg and X_F for biotite. No effect was found for different crystallographic orientations. SIMS analysis allows the oxygen isotope composition of biotite to be measured with a measurement uncertainty of 0.3–0.4‰ (2s) for biotites with similar major element compositions. A measurement uncertainty of 0.5‰ (2s) is realistic when F poor biotites (lower than 0.2% m/m oxides) within the compositional range of X_Mg of 0.3–0.9 were compared from different sessions. The linear correlation with F content offers a reasonable working curve for F‐rich biotites, but additional reference materials are needed to confirm the model.     

Measuring the benefits and costs of community education and outreach in marine protected areas

Conservation organizations often invest considerable resources in education and outreach activities in and around marine protected areas (MPAs). The expectation is that such efforts will change local knowledge, attitudes and ultimately behavior. This is one of the first studies to assess the efficacy of using education and outreach activities to improve community knowledge and attitudes about an MPA. Random sample surveys in 2005 and 2010 (n=1213) before and after education and outreach activities are compared. Program budgets for the same period give the investment levels. With an investment level averaging US$24 per capita/year, the result was an average increase of 33% in “yes” responses across 15 indicators of knowledge and attitudes towards marine conservation. The increase in knowledge and positive attitudes was associated with a large decrease in “not sure” responses, suggesting that community members with fewer initial preconceptions are the most effective target for education and outreach activities. This study demonstrates that investments in MPA education and outreach can generate increases in local knowledge and positive attitudes, and changing knowledge and attitudes is expected to contribute to the long-term compliance with MPA regulations.     

Dykes, faults and palaeostresses in the Teno and Anaga massifs of Tenerife (Canary Islands)

A structural field study was made of 578 sheet intrusions (mostly dykes) and 153 (mostly normal) faults dissecting the Anaga and Teno massifs, where a complex volcanic succession of Tertiary age (the ‘Old Basaltic Series’) representing the shield-building stage of Tenerife (Canary Islands) crops out. Many of the intrusions, mostly sub-vertical mafic dykes, are emplaced by multiple magma injections, with cumulative thicknesses mostly less than 2 m. Dyke tips are exposed and preserved for 12% of the dykes. Three differently oriented sets of dykes exist in the Anaga massif (NNW–SSE, NNE–SSW, E–W), whereas there is only one main set in Teno, trending NNW–SSE. Dyke swarms and other structural features having similar orientations also exist in other Canary Islands. A minimum value of the horizontal component of extension induced by dykes is computed using a step of 5° of azimuth, accounting also for the dip of dykes. The cumulative crustal dilation is at least 300 m (4%) in Anaga and 270 m (6%) in Teno; the maximum extension peaks at N75° in Anaga and N60° in Teno, indicating a general prevailing extension in direction ENE–WSW. Most of the measured faults are normal and strike NNW–SSE. Computation of palaeostresses from inversion of fault-slip data sets suggests the existence of a polyphase brittle deformation due to an extensional stress field with the minimum compressive principal axes trending NE–SW and WNW–ESE.     

Relation between mean stress,thermodynamic, and lithostatic pressure

Pressure is one of the most important parameters to be quantified in geological problems. However, in metamorphic systems the pressure is usually calculated with two different approaches. One pressure calculation is based on petrological phase equilibria and this pressure is often termed thermodynamic pressure. The other calculation is based on continuum mechanics, which provides a mean stress that is commonly used to estimate the thermodynamic pressure. Both thermodynamic pressure calculations can be justified by the accuracy and applicability of the results. Here, we consider systems with low‐differential stress (<1 kbar) and no irreversible volumetric deformation, and refer to them as conventional systems. We investigate the relationship between mean stress and thermodynamic pressure. We discuss the meaning of thermodynamic pressure and its calculation for irreversible processes such as viscous deformation and heat conduction, which exhibit entropy production. Moreover, it is demonstrated that the mean stress for incompressible viscous deformation is essentially equal to the mean stress for the corresponding viscous deformation with elastic compressibility, if the characteristic time of deformation is five times longer than the Maxwell viscoelastic relaxation time that is equal to the ratio of shear viscosity to bulk modulus. For typical lithospheric rocks, this Maxwell time is smaller than c. 10,000 years. Therefore, numerical simulations of long‐term (>10 kyr) geodynamic processes, employing incompressible deformation, provide mean stress values that are close to the mean‐stress value associated with elastic compressibility. Finally, we show that for conventional systems the mean stress is essentially equal to the thermodynamic pressure. However, mean stress and, hence, thermodynamic pressure can be significantly different from the lithostatic pressure.     

Tjörnes fracture zone. New and old seismic evidences for the link between the North Iceland rift zone and the Mid-Atlantic ridge

The Tjörnes facture zone (TFZ) connects the EW extension of the Mid-Atlantic ridge north of Iceland to the extension of the North volcanic zone (NVZ) of Iceland. Earthquakes up to magnitude 7 (Ms) can occur in TFZ, volcanic eruptions have been observed and large crustal deformations are expected in similar way as have been observed in the NVZ. Most of the zone is below ocean, which limits the historical information and geological observations. For studying the dynamics of the zone we must rely on interpretation and modelling based on seismic observations, especially on microearthquake observations for the last 10 years. In this paper we demonstrate how microearthquakes can be applied to map the details of the plate boundary, and how this information can be applied to find epicenters and fault planes of large historical earthquakes, also how seismic information can be applied in dynamic modelling and to infer spatial and temporal interplay in activity, and to enhance hazard assessment.